Java 显示数据库MySQL中保存的消息

我创建了一个关于spring boot的聊天。几个人可以通信的地方。因此，我创建了一个数据库，并在那里存储来自用户的所有消息。所以我想，如果一个新用户进入聊天室，那么他应该只看到最后10条消息。问题是程序没有从数据库获取最后10条消息，而是从服务器获取，这是不正确的。我要他从数据库中提取最后10条信息

我的代码

休息控制器

@SpringComponent
@org.springframework.web.bind.annotation.RestController
public class RestController {
    private List<Message> store;

    public RestController() {
        store = new ArrayList<>();
    }

    @PutMapping("/api/save")
    public void saveMessage(@RequestBody String chatMessage) {
        store.add(new Gson().fromJson(chatMessage, Message.class));

        if (store.size() > 10)
            store.remove(0);
    }

    @GetMapping("/api/last")
    public String getLasts() {
        return new Gson().toJson(store);
    }
}

server.port=8080
# This is a workaround for https://github.com/vaadin/spring/issues/381
spring.servlet.multipart.enabled = false

spring.datasource.url=jdbc:mysql://localhost:3306/chat?createDatabaseIfNotExist=true&serverTimezone=UTC
spring.datasource.username=root
spring.datasource.password=123456

spring.jpa.hibernate.ddl-auto=update
spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true

spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

消息存储库

@Repository
public interface MessageRepository extends JpaRepository<Message, Long> {
}

应用程序控制器

@SpringComponent
@org.springframework.web.bind.annotation.RestController
public class RestController {
    private List<Message> store;

    public RestController() {
        store = new ArrayList<>();
    }

    @PutMapping("/api/save")
    public void saveMessage(@RequestBody String chatMessage) {
        store.add(new Gson().fromJson(chatMessage, Message.class));

        if (store.size() > 10)
            store.remove(0);
    }

    @GetMapping("/api/last")
    public String getLasts() {
        return new Gson().toJson(store);
    }
}

server.port=8080
# This is a workaround for https://github.com/vaadin/spring/issues/381
spring.servlet.multipart.enabled = false

spring.datasource.url=jdbc:mysql://localhost:3306/chat?createDatabaseIfNotExist=true&serverTimezone=UTC
spring.datasource.username=root
spring.datasource.password=123456

spring.jpa.hibernate.ddl-auto=update
spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true

spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

---

坦率地说，我不理解在控制器中存储对象的目的。如果要查询最后10条消息，只需在存储库中实现一个方法并在控制器中调用它即可

MessageRepository

@Repository
public interface MessageRepository extends JpaRepository<Message, Long> {
  List<Message> findTop10ByOrderByTimeDesc();
}

@存储库
公共接口MessageRepository扩展了JpaRepository{
列出findTop10ByOrderByTimeDesc（）；
}

尝试在RestController.getLasts（）中获取最后10条消息，而不是整个存储对象。您可以携带代码。您可以使用Page和Pageable，因此添加api@ApiParam Pageable Pageable，您的存储库应该是公共接口MessageRepository extensed JpaRepository，JpaSpecificationExecutor{}只需在rest页面Page=pkoCategoryRequirementRepository.findAll（可分页）中给他打电话；getLasts（）{return new Gson（）.toJson（store.subList（Math.max（store.size（）-10,0），store.size（））；}这是不正确的((

server.port=8080
# This is a workaround for https://github.com/vaadin/spring/issues/381
spring.servlet.multipart.enabled = false

spring.datasource.url=jdbc:mysql://localhost:3306/chat?createDatabaseIfNotExist=true&serverTimezone=UTC
spring.datasource.username=root
spring.datasource.password=123456

spring.jpa.hibernate.ddl-auto=update
spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true

spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

@Repository
public interface MessageRepository extends JpaRepository<Message, Long> {
  List<Message> findTop10ByOrderByTimeDesc();
}